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The big problem with Fischer Tropsch is the wasted energy. Solid oxide fuel cells can directly turn carbon dioxide into carbon monoxide with a little bit of ele

The big problem with Fischer Tropsch is the wasted energy. Solid oxide fuel cells can directly turn carbon dioxide into carbon monoxide with a little bit of electrical current, but that last oxygen atom comes off in the Fischer Tropsch reactor where it is far more likely to bind with hydrogen than it is to another oxygen molecule. This essentially means that half the hydrogen you electrolyze is going to end up back as water again. That's a lot of wasted electricity. Biomass has potential through Fischer Tropsch though. Not much use on an aircraft carrier, but way more energy efficient to produce syngas with biomass.

dredmorbius 7y ago
I don't know the chemistry all that well (other than the net overall balance). But if there are alternative pathways ... that could be useful. I do believe that there are catalysts (generally iron, thankfully not very exotic) involved. There's also the Sabatier process, which yields methane rather than liquid fuels. I believe that can be further processed to arrive at longer-chain hydrocarbons. HC6-HC10 chains are roughly petrol/gasoline, HC12 is about kerosene, and HC16 or so roughly diesel, as I understand. Methane is CH4. The problem with biomass is that our present energy demands are immense. A sufficient amount for military aviation needs, possibly. Enough to sustain present levels of commercial and private aviation: no. HANPP / the photosynthetic ceiling is a real bitch. https://old.reddit.com/r/dredmorbius/comments/2cvap7/the_intractable_problem_of_biomass_for_fuels_is/ https://old.reddit.com/r/dredmorbius/comments/2cvap7/the_int... Boeing claimed a major "breakthrough" some years back. It ... doesn't add up: https://old.reddit.com/r/dredmorbius/comments/1wo2hl/boeings_biofuel_breakthrough_less_than/ https://old.reddit.com/r/dredmorbius/comments/1wo2hl/boeings... When I'd first started looking at fuel concerns, I'd thought biofuels offered a viable path out. I'm utterly convinced they don't. At least not for a world with 1-7 billion drivers. Maybe with 100 million cars. Henry Ford suggested alcohol, from grains, as a fuel circa 1900. At the time, 20% of US grain production was dedicated to transport, though utilising a somewhat different prime mover: horses.
- philipkglass 7y ago
  When electricity from solar and wind power were much more expensive, biomass looked attractive as a lower cost (if limited-availability) energy source. I'd say that it is still potentially attractive for making liquid fuels, but less because of its embodied energy content and more as a compact source of carbon that has recently been removed from the atmosphere. Cellulosic ethanol is pretty terrible even when the process is operating as planned: http://www.ethanolproducer.com/articles/15344/zero-to-10-million-in-5-years http://www.ethanolproducer.com/articles/15344/zero-to-10-mil... 70 gallons of ethanol from 1 short ton of cellulose means 230 kg from 1000 kg of cellulose. There's 444 kg of carbon in that much cellulose, enough to make 518 kg of diesel fuel if given enough externally supplied hydrogen. The energy content of the final fuel from 1 tonne of cellulose is 23.6 GJ for diesel and only 6.9 GJ for the ethanol. Liquid biofuels from non-cellulosic inputs have even worse areal productivity. (Barring (theoretically) algae, which nobody seems to be able to implement at industrial scale.) US airline fuel consumption peaked in 2007 at 20 billion gallons per year: https://www.eia.gov/todayinenergy/detail.php?id=31512 https://www.eia.gov/todayinenergy/detail.php?id=31512 That's about 63 million tonnes of kerosene/diesel. You'd need at least 122 million tonnes of cellulosic biomass to supply carbon for that much fuel. You'd also need refiners, crackers, and recapture in addition to F-T units to ensure that both too-light and too-heavy carbon compounds get recycled to produce liquid hydrocarbons of the desired saturation and molecular weight. It would basically be running a state of the art petrochemical complex with biomass gasifiers and electrolytic hydrogen bolted on. But assuming you did all that, the raw material availability looks relatively favorable. As of 2005, this report estimated that over 300 million tonnes of currently-unused dry biomass could be sustainably harvested from forests and agricultural wastes: https://www1.eere.energy.gov/bioenergy/pdfs/final_billionton_vision_report2.pdf https://www1.eere.energy.gov/bioenergy/pdfs/final_billionton...
  - dredmorbius 7y ago
    I can confirm pretty much all of that from my own research, with most of those topics / technologies at least touched on at https://old.reddit.com/r/dredmorbius https://old.reddit.com/r/dredmorbius The fact of peak US aviation fuel surprised the heck out of me when I stumbled across it. I'm holding out hopes for wind/solar feeding F-T for at least some liquid fuels production.

dredmorbius 7y ago

I don't know the chemistry all that well (other than the net overall balance). But if there are alternative pathways ... that could be useful. I do believe that there are catalysts (generally iron, thankfully not very exotic) involved. There's also the Sabatier process, which yields methane rather than liquid fuels. I believe that can be further processed to arrive at longer-chain hydrocarbons. HC6-HC10 chains are roughly petrol/gasoline, HC12 is about kerosene, and HC16 or so roughly diesel, as I understand. Methane is CH4. The problem with biomass is that our present energy demands are immense. A sufficient amount for military aviation needs, possibly. Enough to sustain present levels of commercial and private aviation: no. HANPP / the photosynthetic ceiling is a real bitch. https://old.reddit.com/r/dredmorbius/comments/2cvap7/the_intractable_problem_of_biomass_for_fuels_is/ https://old.reddit.com/r/dredmorbius/comments/2cvap7/the_int... Boeing claimed a major "breakthrough" some years back. It ... doesn't add up: https://old.reddit.com/r/dredmorbius/comments/1wo2hl/boeings_biofuel_breakthrough_less_than/ https://old.reddit.com/r/dredmorbius/comments/1wo2hl/boeings... When I'd first started looking at fuel concerns, I'd thought biofuels offered a viable path out. I'm utterly convinced they don't. At least not for a world with 1-7 billion drivers. Maybe with 100 million cars. Henry Ford suggested alcohol, from grains, as a fuel circa 1900. At the time, 20% of US grain production was dedicated to transport, though utilising a somewhat different prime mover: horses.

philipkglass 7y ago
When electricity from solar and wind power were much more expensive, biomass looked attractive as a lower cost (if limited-availability) energy source. I'd say that it is still potentially attractive for making liquid fuels, but less because of its embodied energy content and more as a compact source of carbon that has recently been removed from the atmosphere. Cellulosic ethanol is pretty terrible even when the process is operating as planned: http://www.ethanolproducer.com/articles/15344/zero-to-10-million-in-5-years http://www.ethanolproducer.com/articles/15344/zero-to-10-mil... 70 gallons of ethanol from 1 short ton of cellulose means 230 kg from 1000 kg of cellulose. There's 444 kg of carbon in that much cellulose, enough to make 518 kg of diesel fuel if given enough externally supplied hydrogen. The energy content of the final fuel from 1 tonne of cellulose is 23.6 GJ for diesel and only 6.9 GJ for the ethanol. Liquid biofuels from non-cellulosic inputs have even worse areal productivity. (Barring (theoretically) algae, which nobody seems to be able to implement at industrial scale.) US airline fuel consumption peaked in 2007 at 20 billion gallons per year: https://www.eia.gov/todayinenergy/detail.php?id=31512 https://www.eia.gov/todayinenergy/detail.php?id=31512 That's about 63 million tonnes of kerosene/diesel. You'd need at least 122 million tonnes of cellulosic biomass to supply carbon for that much fuel. You'd also need refiners, crackers, and recapture in addition to F-T units to ensure that both too-light and too-heavy carbon compounds get recycled to produce liquid hydrocarbons of the desired saturation and molecular weight. It would basically be running a state of the art petrochemical complex with biomass gasifiers and electrolytic hydrogen bolted on. But assuming you did all that, the raw material availability looks relatively favorable. As of 2005, this report estimated that over 300 million tonnes of currently-unused dry biomass could be sustainably harvested from forests and agricultural wastes: https://www1.eere.energy.gov/bioenergy/pdfs/final_billionton_vision_report2.pdf https://www1.eere.energy.gov/bioenergy/pdfs/final_billionton...
- dredmorbius 7y ago
  I can confirm pretty much all of that from my own research, with most of those topics / technologies at least touched on at https://old.reddit.com/r/dredmorbius https://old.reddit.com/r/dredmorbius The fact of peak US aviation fuel surprised the heck out of me when I stumbled across it. I'm holding out hopes for wind/solar feeding F-T for at least some liquid fuels production.